Solar energy is a popular clean energy, but it is generally more expensive than its carbon based competitors (e.g., oil, coal, and natural gas) and other traditional non-carbon based energy sources (e.g., hydropower). Typically, solar energy is also relatively expensive because traditional photovoltaic cells with a planar configuration have generally low total efficiency. Total efficiency is based upon the total power produced from a solar cell throughout the day as the sun transits across the sky. Total efficiency is different from the theoretical efficiency of converting to electricity a given amount of light energy striking the photovoltaic cells with a zero angle of incidence (e.g., the instant when the sun is directly above the solar cell).